Photoelectric storage device



1940- K. SCHLESINGER 3 PHOTOELECTRIC STORQGE DEVICE Filed June 11, 1937fnrepfar;

Patented Dec. 31, 1940 rno'roELEo'r PATENT OFFICE mo STORAGE DEVTCE KurtSchlesinger, Berlin, Germany, assignor, by

mesne assignments, t

poration of New York Application June 11,

In Germany June 16, 1936 1 1 Claim.

The applicant has formerly proposed to employ a device. for storing, andscanning photoelectric charges which device consists in substance of acoherent andan incoherentphotoelectric plate electrode,.for example amesh and a mosaic screen. The two plates are situated opposite andparallel to I one another, and the photo-electric condenser thus formedis from the one side illuminated by the image light and from the otherside scannedby a moving spot of light, which in turn may be produced, asa projection of the luminous screen image of a television cathode raytube. Thisarrangement, while yielding quite satisfactory effects in thetelevision transmission of scenes, is still subject to internal losses.These losses are due primarily to the fact thatthe two illuminationsinfluence one another because none of them is completely absorbed by theelectrode on which it impinges and each of them causes,

.29 partly reflected, a spurious discharge of the other electrode, sothat the storage duced. 1

"An object of the present invention is. a tube construction avoiding theabove disadvantage.

A further object of the invention is a tube act- 'ing in itself as anelectronic amplifier of 'the current obtained by scanning the image.

The invention will be explained by 'meansof the accompanying drawing ofwhich Fig. 1 shows an arrangement according to the invention, 1 I

Fig. 2 is a detailed cross-section of electrodes according to theinvention includingthe circuit connectedtherewith, Fig. 3 shows amodified circuit connection of the electrodes of the device according to:Fig. 1, and

Fig. 4 the structure illustrated'in Fig. 1 as com bined with an electronamplifier system.

In Fig. 1, I is a network having a number of meshes which corresponds atleast to the number of image points. The network consists of silver, oris silver-coated, and is photo-electrically activated in the usualmanner by means of caesium. 45 It functions as photo-electric cathode.In close proximity opposite to 1 there is provided a mosaic screen 2,which consists of at least as many small rods as there are image pointsto be transmitted. The rods are photo-electrically activated on its 50rear side and are well insulated one against the other. Behind thescreen 2, at a somewhat larger distance, there is arranged an anode 3consisting of a wide network of thin wires. The whole assembly isenclosed within the vacuum vessel 4. 55 The image or scene 5 isprojected onto the front output will be reo Loewe'RadioJncs a cor- 1937,Serial No.147,7 99

side of the'net I by way of a lens 6, whilst the rear side of thescreen2 is scanned by a light spot projected onto it by means of thelens I from the luminousscreen of a Braun tube 8 operated in the wellknown manner with constant ray inelectron emission of the correspondingpoint of I according to the light intensity of each point, and thisemission is absorbed the. rods 2 forming anodes with respect to I.. Thepositive charges of the rods are due to the scanning light spot freeingelectrons from the rods. Thuseach rod facingan illuminated part of thenet I will, when recharged bythe scanning spot, cause a current pushthrough'resistance 9 which is coupled at 2| to the videoamplifier (notshown). c c It is accordingly on the one hand necessaryto make the.capacity between I and 2 very. large, whilst on the other hand 'it isvery detrimental to 'allovv'jalarge capacity between the different rods2.. In practice it would be very diificult to fulfil this conditionwithout employing the .construction ofthe screen according to Fig. 2. Ia In Fig.. 2,. 2a is a cross section through a coherent net or sieveinsulated on all sides. An appropriate insulation, when employing asieve of aluminium, may be produced advantageously by an electricaloxidizing process. It is, however, also possible toemploy. anyother'metal and to glaze the same," for example with enamel. Theinsulation of the. sieve is represented by the surrounding curves II.After this operation. metallic silver is introduced into theintermediate spaces of the sieve, so as to completely fill out thepreviously open meshes. The silver is designated I 212. It replaces therods 2 inFig. 1'. The introe ,ductionfof the silver may take place, forexample, by reducing a paste of silver compound at high temperature orelectrolytically or by atomization. After the introduction of themetallic plugs 2b the same are photo-electrically activated on the sidefacing the anode 3. The supporting sieve 2a is, by means of lead I2,electrically connected with the net I and this way earthed, thisscreening-off the singled rods 2b against each other. The spacingbetween screen 2 and net I must, accordingly be equal to or smaller thanthe mesh width in order to avoid a straying of the primary electronsfrom one image point location to adjacent ones. In practice, even withthe maximum number of lines presently used, i. e., with 400 lines, aspacing of mm. will be found suiliowing to the fact that the scanninglight drops off the area. In this way novel effects maybe obtained inthe transmission of images.

Instead of coupling the amplifier tothe anode 3 it may also, with thereciprocal efiect be coupled at 3| by means of a resistance 22 to thenet I, according to Fig. 3, with the disadvantage that a condenser l3must be inserted in order toblock-' off the direct current.

A particularly important feature is the possibility of directlyamplifying the electron currents supplied by plate 2 before they areconducted to a tube amplifier. In contradistinction' to the knownikonoscope this screen plate supplies electron currents instead ofvoltage impulses, which electron currents may be directly multiplied bysecondary current multiplication. whereby the ratio between signals,andinoises is considerably reduced. For this purpose itis firstlynecessary to concentrate the electrons, which'are leaving the largearea2 by means of an electron-optical collecting lens on to a comparativelysmall focus point. As the applicant has found, this may be effected by,the use offtwo co-axial ringslfi, l (Fig. 4) in conjunction with ananode ring I6. The height of the rings I4 is approximately equal totheirradius. Thev first ring M is connected with a weak positivepotentialofabout volts relatively to earth. The next ring l5. and theanode ring 5 are furnished with increasing potentials By adjusting ofthe intermediate potential IE it is possible to concentrate allelectronic raysiust in or behind the aperture of i6 into a space tentimes smaller than the area 2. At this point there may be provided asmall intermediate anode. H, which becomes the origin of an.amplifiednumber of electrons. Methodsof magnetically 'or electricallyseparating the primary and secondary electron rays. are already known.An. electric or magnetic deflection of the primary rays may also takeplace before the impinging on IT, for example, tothe extent of 90, bymeans of a magnetic fieldinot shown) disposed perpendicularly, to theplane of the paper, so that the next intermediate. anode is situated atis and the. secondary electrons emitted from the latter impinge ,on 2 3.The last anode is connected to thefmost positive'term'inal of thebattery It, the intermediate anodes to progressive intermediatepotentials, and'theoutput 2| to the signal amplifier. Infthisarrangement the anodes are so disposed that the screen 2 is freelyaccessible to the light from the scanned area projected into the tube bythe lens 1.

I claim:

A television system comprising an evacuated tube member, aphotoelectrically activated meshlike electrode element within the tube,a connection from said element to a point 'ofequilibrium potential,means to illuminate said element with the light of an optical image torelease photoelectrons therefrom, a mosaic electrode element within thetube in close proximity to and substantially parallel to said mesh-likeelement to collect electrons released from the mesh-like element underthe influence of light, said mosaic element also comprising a mesh-likesupport and having an insulating coating about the mesh and metallicelements extending within and protruding through the interstices of themesh to a plane at least, co-planar with the plane of the mesh, saidmetallic elements being insulated one from the other by" theinsulatingcoating, a photoelectric coating upon the ends of the metallicelements which are remote from the photoelectrically activated mesh-likeelectrode, an apertured anode element, a source of scanning light toilluminate the photoelectrically activated areas of the mosaic accordingto a. predetermined light traversal pattern and to release electronstherefrom at areas of light impingement, thequantity ofelectrons'instantaneously released by the scanning light being measuredby the amount necessary to raise the potential of the mosaic element tosubstantially anode potential from a more negativevalue due tocollecting photoelectrons from the mesh-likeelectrode element, a secondanode element of an area relatively smallcompared to the mosaicelectrodeelement, means to maintain the second anode positivewithres'pect to the first anode, focusing electrode. means intermediatethe mosaic and the first anode to focus the electrons released from themosaic by the scanning light through the first apertured anode and uponthe second anode so that the electron stream released from therelatively large mosaic area is concentrated upon the reduced .area'second anode and secondary electrons. are released therefrom by theimpact thereon'ofthe said initialy released electrons, said second anodebeing in non-parallel relation relative to the mosaic to redirect theelectron flow reaching said second anode along a diverted path,electrode means for producing by secondary emissionfurtherintensification of the electron flow, an output electrode and a directconnected load circuit for amplifying the resultant output energyavailable at theoutput electrode. 1 I 1 KURT S CHLESINGER.

